Oil leak

I recently changed the head gaskets and timing chain. After putting everything back together, I cranked it up and it ran just fine. However, oil began to leak from the engine like a waterfall! I looked underneath the vehicle and it seemed to be coming from the rear top of the engine, but I could not see from exactly where. I went to the top of the engine and put my hand around the back of the engine to try to feel where the leak might be. I felt that the oil was "puddling" under the intake manifold between the heads. Did I miss a step in the re-assembly, did not tighten something at the right torque or has something gone bad like a seal? Why would oil puddle under the intake manifold? Would it leak somewhere from one of the heads. If it was cracked?